misc: make export directory creation recursive

src/script/functions/export.cpp

@@ -54,10 +54,11 @@ String get_export_full_path(String& rel_name) {
   return fn.GetFullPath();
 }
 
-void ensure_dir_valid(String& path) {
-  wxFileName filename = path;
-  if (!filename.DirExists())
-    filename.Mkdir();
+void ensure_dir_valid(String& path) {
+  if (!wxDirExists(path)) {
+    wxFileName filename = path;
+    filename.Mkdir(wxS_DIR_DEFAULT, wxPATH_MKDIR_FULL);
+  }
 }
 
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